1. Technical Field
The present invention relates to a semiconductor device, and more particularly, to a method for manufacturing a semiconductor device, in which a solvent of a bottom antireflective coating film is completely removed using a porous material so as to prevent acid in a photoresist film from reacting with the solvent during a post exposure baking (PEB) process.
2. Discussion of the Related Art
Previously, for an exposure process using a light source in the mid ultra violet (MUV) region of the spectrum, only a photoresist film had been coated on a wafer prior to the wafer undergoing an exposure process.
Recently, a light source such as KrF, in the deep ultra violet (DUV) region of the spectrum, is being used to form a fine pattern. In this case, a bottom anti reflective coating (BARC) film is formed below the photoresist film to solve a problem that occurs when light enters the wafer below the photoresist film. In the case where a DUV light source has a short wavelength, the DUV is reflected on the wafer through the photoresist film and causes interference with the incident light. For this reason, a standing wave is generated, which prevents the photoresist film from forming with a uniform profile. That is, the bottom antireflective coating film serves to prevent the light, which has passed through the photoresist film, from being externally reflected.
The bottom antireflective coating film is mainly used to obtain a uniform critical dimension (CD) depending on a predetermined thickness of the photoresist film pattern. In other words, if no bottom antireflective coating film is used, a scanned KrF laser is only reflected on the wafer and then emitted to the outside through the photoresist film pattern. At this time, an offset reaction generates a standing wave that prevents the photoresist film pattern from forming a uniform vertical profile. Instead, the vertical sides of the photoresist film are formed with the shape of a sine curve, as a result of the generated standing wave. The bottom antireflective coating film is used to prevent the standing wave from occurring and enable the formation of a photoresist film pattern having a substantially uniform vertical profile.
Hereinafter, a related art method for manufacturing a semiconductor device will be described with reference to the accompanying drawings.
FIG. 1 is a sectional view illustrating a photoresist film coated, exposed and developed on a wafer having no bottom antireflective coating film.
As shown in FIG. 1, a photoresist film is coated on a wafer 10 without a bottom antireflective coating film. The photoresist film is then exposed and developed. Incident light onto the wafer 10 through the photoresist film is reflected on a surface of the wafer 10 and interferes with additional incident light. For this reason, a portion of the pattern is not uniformly exposed, and light is not uniformly irradiated onto a side of the exposed portion. Therefore, a rough side of a photoresist film pattern 1 is formed after the portion of the pattern is developed. This means that the photoresist film pattern 1 has different critical dimensions depending on its thickness. Meanwhile, if the photoresist film is formed of a positive photoresist material, the exposed portion will be removed. If the photoresist film is formed of a negative photoresist material, the exposed portion will remain.
FIG. 2 illustrates the variation in the width of the photoresist film depending on its thickness if a bottom antireflective coating film is formed, and FIG. 3 illustrates the variation in the width of the photoresist film depending on its thickness if no bottom antireflective coating film is formed.
As shown in FIG. 2, if the bottom antireflective coating film is formed below the photoresist film, it is noted that the width of the photoresist film pattern formed by exposure and developing processes linearly increases as the thickness (height of the photoresist film formed from on the surface of the wafer) of the photoresist film increases.
However, as shown in FIG. 3, if no bottom antireflective coating film is formed below the photoresist film, it is noted that the width of the photoresist film pattern formed by exposure and developing processes increases at a certain time period but irregularly increases or decreases without linearly increasing within the period as the thickness of the photoresist film increases.
In other words, if the photoresist film pattern is formed by exposure and developing processes without a bottom antireflective coating film, it is noted that a vertical side profile of the photoresist film pattern has a sine curve as shown in FIG. 1.
Furthermore, as shown in FIG. 3, variation of the critical dimensions occur depending on the thickness of the photoresist film within a certain time period when a bottom antireflective coating film is not formed.
For this reason, if a fine pattern having a small design rule is formed, it is desirable to use a bottom antireflective coating film in order to form a photoresist pattern having a uniform profile.
As described further below, the bottom antireflective coating film is formed on the wafer by spin coating.
First, a material for the bottom antireflective coating film is dissolved in a solvent. After the material is coated on the wafer, the wafer is rotated to coat the material thereon at a uniform thickness.
Subsequently, baking is performed to evaporate the solvent. At this time, if the solvent is not completely removed by baking, a proper critical dimension is not obtained. Therefore, in the process of manufacturing a semiconductor device using the bottom antireflective coating film, the solvent should be removed completely by baking.
FIG. 4 is a scanning electron microscope (SEM) view illustrating that footing is generated as the solvent remains in the bottom antireflective coating film, and FIG. 5 is a sectional view of FIG. 4.
In the related art process of removing the solvent included in the bottom antireflective coating film after coating the bottom antireflective coating film, as shown in FIGS. 4 and 5, a hot plate is arranged below the wafer 10 and then heated to evaporate the solvent. Thus, the solvent is removed.
FIGS. 4 and 5 illustrate that footing is generated as the solvent remains in the bottom antireflective coating film.
The photoresist film 13 used for a light source, i.e., KrF, is decomposed by acid H+ 15 contained in a developer during a developing process after an exposure process. However, the bottom antireflective coating film 11 in which the solvent remains is combined with the acid H+ which penetrates into the photoresist film 13 to neutralize the acid H+.
As a result, since the acid component that decomposes the photoresist film 13 is removed, the photoresist film 13 at the neutralized portion remains after the developing process. In this case, the critical dimension at the top of the photoresist film 13 becomes different from that at the bottom thereof, generating the footing as shown in FIG. 4.
The method for manufacturing a semiconductor device has the following problems.
The solvent contained in the bottom antireflective coating film is volatile and is evaporated by heat. Therefore, the solvent can be removed completely after baking the wafer for a sufficient length of time. If baking time is reduced, however, productivity can be improved. Therefore, it is important that the solvent be evaporated completely within a short amount of time so as to prevent degradation of the device from occurring, and to increase productivity and yield. However, in the related art process, the baking time is long.
Furthermore, the photoresist film used for a light source, i.e., KrF, is decomposed by the acid H+ contained in the developer during the developing process after the exposure process. However, the bottom antireflective coating film in which the solvent remains is combined with the acid H+ penetrated into the photoresist film and neutralizes the acid H+.
As a result, since the acid component that decomposes the photoresist film is neutralized in portions in the proximity of the antireflective coating film, the photoresist film at the neutralized portion remains after the developing process. In this case, a problem occurs in that the critical dimension at the top of the photoresist film becomes different from that at the bottom thereof. To solve this problem, it is necessary to completely remove the solvent in the bottom antireflective coating film. A new baking process is required, which can evaporate the solvent within a short time to improve productivity.